The present invention is directed to a sheet supporting arrangement to be used in a stacker, especially a stacker which is designed to receive die-cuts, boards or paperboard boxes. The stacker comprises an upper and lower sheet support grid made up of rods of jacks or actuators which are arranged on a front and rear wall of the stacker.
in practical use, stackers for corrugated board sheets are known to work jointly with belts carrying the sheets up to the stacker. These carrying belts are generally arranged so as to drop the sheets on top of the stacker in which the sheets will fall due to the force of gravity.
A stacker of this type is described in U.S. Pat. No. 5,201,513, whose disclosure is incorporated herein by reference thereto and which claims priority from French Patent Application 91 02522. The stacker in this patent includes, among other elements, a front and rear wall on which jacks or pneumatic actuators are arranged. The actuators have rods, and when put in a forward position, the rods make up a first sheet supporting grid which allows the removal of the first sheet piled previously built up on a second supporting grid also made up of rods of other pneumatic jacks equally arranged on the front and rear walls. The removal of the pile thus built up on the second grid is ensured by a roller carrier once the rods of the jacks of the second grid have been retracted to a retracted position to allow the stack to drop onto the roller carrier.
The jacks used in the above-mentioned device are conventional jacks which are sold on the market. More specifically, their rods are of metal and, hence, very rigid.
In use, it has been noticed that when a jam occurs in the course of a high-speed job, the rigidity of the metal rods constitutes a disadvantage that was non-neglectable by the fact that the accumulation of sheets between the first grid made up of rods of the jacks, which is the upper grid, and the carrier belts was causing considerable damage to the rods of the pneumatic jacks. This damage went, in some cases, to actual breaking of the rods. Moreover, the action of setting the device back into operation after a jam occurred proved to be very difficult, due to the squeezing or pressing of sheets between the grid and the carrier belts, which squeezing or pressing impairs the easy retraction of the rods of each of the pneumatic jacks. Thus, the rods would be more or less bent or squeezed in their guide-pieces of the respective jacks.
In certain cases, the rods of the jacks have even suffered permanent deformation to such a degree that it was almost impossible to retract the rods back into the jacks.